Hello,
The node specifies that the character leaves behind a trail of fire that ignites enemies each second. The trail itself lasts for a few seconds until it starts to dissipate, however even while on, enemies walking on it that are further than the active area of warpath do not get a stack of ignite.
And as such, enemies could be walking a bit further behind, literally walking on fire, and be fine.
Sometimes though, one might start to catch ignite stacks.
It does however works when the enemies are in the warpath active area.
Thank you and have a good day.